1. Field of the Invention
The present invention concerns breathing apparatus, and is particularly concerned with a breathing apparatus which has: a mask having an exhalation orifice and an inhalation orifice, an exhalation space which communicates with the first orifice via an exhalation duct and receives exhaled air, a regenerating arrangement which is connected to the said space and through which the used air flows, an inhalation space which is connected to the said regenerator so that it may receive regenerated air and, via an inhalation duct to the second orifice mentioned above, a source of unused air under pressure, and means to feed air from the said source into the breathing circuit formed by the mask, the said spaces and the said regenerator in such a way as to draw regenerated air into circulation in the said circuit.
Such apparatus is normally intended for use on the ground to protect persons who have to enter dangerous atmospheres such as radioactive or heavily polluted atmospheres which may be encountered in chemical or nuclear industries in mines, and so on.
2. Description of the Prior Art
In known closed circuit breathing apparatus, in the course of the inhalation phase the pressure of the air in the mask in the region of the mouth becomes lower than the pressure of the external atmosphere. The apparatus in question is thus subject to extremely dangerous leaks and the outside atmosphere, which is often dangerous, may enter the mask and even the entire breathing circuit. In addition, the reduced pressure inside the mask means that there is insufficient breathing air reaching the user, which may cause him considerable inconvenience.
The present invention has as a primary object to overcome these disadvantages. A further object of the invention is to provide a closed-circuit breathing apparatus in which there is a constant over-pressure in the breathing circuit of the apparatus relative to the external medium.